Light emitting device provided with lens for controlling light distribution characteristic

ABSTRACT

The light emitting device comprises a substrate ( 2 ), a positive electrode ( 6 ) and a negative electrode ( 4 ) formed on the substrate ( 2 ), a light emitting diode ( 8 ) connected to the positive electrode ( 6 ) and the negative electrode ( 4 ), the transparent resin ( 12  and  14 ) that covers the light emitting diode ( 8 ), a fluorescent material ( 16 ) that absorbs at least part of light emitted by the light emitting diode ( 8 ) and converts it to light of longer wavelength, and the lens that changes the direction of light emission from the light emitting diode ( 8 ) and/or the fluorescent material ( 16 ). The resin ( 12  and  14 ) includes the fluorescent material ( 16 ) and is formed so as to constitute the lens of substantially semi-cylindrical shape, and the fluorescent material ( 16 ) included in the resin ( 12  and  14 ) is distributed with a higher concentration in a region near the surface of the light emitting diode ( 8 ) than in a region near the surface of the portion that constitutes the lens.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of co-pending U.S. applicationSer. No. 12/473,121 filed May 27, 2009, which in turn claims priority on37 C.F.R. §1.53(b) divisional of U.S. application Ser. No. 11/356,276filed Feb. 17, 2006, now U.S. Pat. No. 7,710,016 issued May 4, 2010,which in turn claims priority on Japanese Application No. 2005-42533filed Feb. 18, 2005 and Japanese Application No. 2005-42543 filed Feb.18, 2005. The entire contents of each of these applications are herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates a light emitting device that is capable ofemitting light of various colors by combining a light emitting diode andfluorescent materials, and particularly to a light emitting device thathas a lens for controlling the light distribution characteristic.

2. Background Art

In recent years, the development of the blue light emitting diode thatutilizes nitride semiconductor has made it possible to manufacture lightemitting devices that emit light of various colors by combining the bluelight emitting diode and fluorescent materials which absorb at leastpart of light emitted by the light emitting diode and emit light ofdifferent color tones. A light emitting diode that emits white light, inparticular, can be made by using a blue light emitting diode as thelight emitting diode and a fluorescent material which absorbs part oflight emitted by the blue light emitting diode and emits light of acolor complementary to blue.

These light emitting devices can be classified into various typesincluding bullet type and surface-mounted type.

A bullet type light emitting device has a cup formed at the distal endof one of positive and negative lead electrodes, and a light emittingdiode mounted in the cup with the cup filled with a resin which includesa fluorescent material dispersed therein. The cup is then surrounded bya molding resin that is formed in a bullet shape having lens-shaped tip(refer to, for example, Japanese Unexamined Patent Publication (Kokai)No. 7-99345).

A surface-mounted type light emitting device has such a constitution asa recess is formed on a substrate having a positive electrode and anegative electrode formed thereon, so that a light emitting diode ismounted in the recess which is then filled with a resin including afluorescent material dispersed therein (refer to, for example, JapaneseUnexamined Patent Publication No. 2002-319711).

When white light is emitted by combining the blue light emitting diodeand a fluorescent material, in particular, color tone of the white lightis determined by the balance between the intensity of light emitted bythe blue light emitting diode and the intensity of light emitted by thefluorescent material. However, since it is difficult to control thequantity of the fluorescent material dispersed in the resin which fillsin the light emitting device, a problem of difference in color tone dueto different amounts of fluorescent material among individual devicesarises. To counter this problem, Japanese Unexamined Patent Publication(Kokai) No. 2001-177158 discloses a method of correcting the differencein color tone by grinding the resin layer that includes the fluorescentmaterial thereby to control the quantity of the fluorescent material.Japanese Unexamined Patent Publication (Kokai) No. 2004-186488 disclosesa method of correcting the difference in color tone by controlling thethickness of the resin layer in a portion which does not include thefluorescent material.

In the light emitting device that combines the light emitting diode andthe fluorescent material, color unevenness often becomes a problem thatthe emitted light show different colors depending on the direction ofview. The color unevenness occurs when the light rays pass throughdifferent amounts of fluorescent material depending on the differentdirections. In order to mitigate the color unevenness between differentdirections of view, therefore, the fluorescent material is preferablyconcentrated in the vicinity of the light emitting diode. For thispurpose, such means have been taken as surrounding the light emittingdiode with a cup that only is filled with a resin including afluorescent material dispersed therein and covering the light emittingdiode and the cup as a whole with a sealing resin layer formed in a lensshape (refer to, for example, Japanese Unexamined Patent Publication(Kokai) No. 10-242513), or dripping a resin that includes a fluorescentmaterial dispersed therein only in a region surrounding the lightemitting diode and, after curing the resin to harden, covering the lightemitting diode and the cup as a whole with a sealing resin layer formedin a lens shape (refer to, for example, Japanese Unexamined PatentPublication (Kokai) No. 2000-315824).

It is also in practice to control the light distribution characteristicof a light emitting device that uses a light emitting diode, by forminga lens on a light transmitting sealing resin layer. The transparentsealing resin layer may be formed, for example, by the followingmethods.

(1) A sealing resin layer is formed into lens shape by molding.

(2) A sealing resin layer formed in a flat plate shape is formed intolens shape by machining.

(3) A lens formed beforehand is attached to the surface of a sealingresin layer.

(4) A casting case is used.

Among these, the method of forming the sealing resin layer into lensshape by molding is simple and suited to volume production, and istherefore widely employed. For molding the resin, it is common to theemploy transfer mold process that is widely applied to the sealing resinlayer for semiconductor chips (refer to, for example, JapaneseUnexamined Patent Publication (Kokai) No. 2000-196000 and JapaneseUnexamined Patent Publication (Kokai) No. 2001-352105).

In recent years, there is increasing demand for lower profile on sideview type light emitting device, which is a kind of surface-mountedlight emitting diode. The side view type light emitting device is alow-profile light emitting diode that emits light from a side facethereof. Many of the side view type light emitting device emit lightfrom a side face that adjoins the mounting surface. There is also ademand for the surface mounted type light emitting device to form theresin layer that constitutes the light emitting surface into a lensshape, so as to provide a favorable light distribution characteristic.However, in case a lens is formed on the light emitting surface of thesurface mounted type light emitting device, there have been suchproblems that the light emitting device becomes larger in size andrequires a complex manufacturing process. When it is attempted tocorrect the difference in color tone by grinding the resin layer thatconstitutes the light emitting surface, as described in JapaneseUnexamined Patent Publication (Kokai) No. 2001-177158 and JapaneseUnexamined Patent Publication (Kokai) No. 2004-186488, there has beensuch a problem that the lens formed on the light emitting surfacedeforms, thus causing the light distribution characteristic to alter.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a light emitting devicehaving a lens formed in a transparent layer that constitutes a lightemitting surface, which is low in profile, has good light distributioncharacteristic, and is easy to manufacture.

The light emitting device according to the first aspect of the presentinvention comprises a substrate, a positive electrode and a negativeelectrode formed on the substrate, a light emitting diode connected tothe positive electrode and the negative electrode, a transparent layerthat covers the light emitting diode, a fluorescent material thatabsorbs at least part of light emitted by the light emitting diode andconverts it to light of a longer wavelength, and a lens that changes thedirection of light emission from the light emitting diode and/or thefluorescent material, wherein the transparent layer includes thefluorescent material and is formed so as to constitute a lens ofsubstantially semi-cylindrical shape, and the fluorescent materialincluded in the resin layer is distributed with a higher concentrationin a region near the surface of the light emitting diode than in aregion near the surface of the portion that constitutes the lens.

The light emitting device according to the second aspect of the presentinvention has a layer of two-layer constitution. That is, the lightemitting device comprises a substrate, positive electrode and a negativeelectrode formed on the substrate, a light emitting diode connected tothe positive electrode and the negative electrode, a transparent layerthat covers the light emitting diode and a fluorescent materialdispersed in the resin, so as to excite the fluorescent materialdispersed in the transparent layer with the light emitted by the lightemitting diode to emit light of a color different from that of the lightemitted by the light emitting diode, wherein the transparent layer thatcovers the light emitting diode and comprises a first transparent layerincluding the fluorescent material and a second transparent layer formedon the first transparent layer, and the second layer is formed to have acurved shape so as to form a lens, while the first transparent layer andthe second transparent layer are cut to have a coplanar face on a pairof opposed side faces of the light emitting device so that the firsttransparent layer is exposed.

The light emitting device according to the third aspect of the presentinvention comprises a substrate, a positive electrode and a negativeelectrode formed on the substrate, a light emitting diode connected tothe positive electrode and the negative electrode, a sealing resin layerthat covers the light emitting diode, a fluorescent material whichabsorbs at least part of light emitted by the light emitting diode andconverts it to light of a longer wavelength, and a lens that changes thedirection of light emission from the light emitting diode and/or thefluorescent material, wherein the sealing resin layer includes thefluorescent material and is formed integrally so as to constitute thelens, and the fluorescent material is distributed with a higherconcentration in a region near the surface of the light emitting diodethan in a region near the surface of that constitutes the sealing resinlayer.

In this application, the term “transparent” means such a level of lighttransmission as the light emitted by the light emitting diode can beobserved from the outside.

The light emitting diode preferably has a nitride semiconductor lightemitting layer that emits ultraviolet ray or blue light. The lightemitting diode that has the nitride semiconductor light emitting layercan emit light of a short wavelength, which means higher energy, withhigh intensity. Thus a light emitting device capable of emitting lightof various color tones with high luminous intensity can be provided bycombining with fluorescent materials.

Particularly when the fluorescent material is caused to emit light byitself or by blending light emitted by the fluorescent material andlight emitted the light emitting diode, a light source can be made thatcan be applied to backlight, flash light, head light, illumination orthe like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a light emitting device accordingto first embodiment of the present invention.

FIG. 2 is a sectional view taken along lines X-X′ of the light emittingdevice shown in FIG. 1.

FIG. 3 is a perspective view schematically showing the light emittingdevice shown in FIG. 1 mounted on a mounting substrate.

FIG. 4 is a sectional view of another example of the light emittingdevice according to the first embodiment.

FIG. 5A is a schematic diagram showing the first transparent resin layerbeing formed by line application process.

FIG. 5B is a plan view showing the first transparent resin layer beingformed by line application process.

FIG. 5C is a sectional view showing the first transparent resin layerbeing formed by line application process.

FIG. 6A is a sectional view showing a variation of the line applicationprocess shown in FIG. 5C.

FIG. 6B is a sectional view showing another variation of the lineapplication process shown in FIG. 5C.

FIG. 6C is a sectional view showing a further another variation of theline application process shown in FIG. 5C.

FIG. 7A is a perspective view schematically showing a package assemblywherein the first transparent resin layer is formed.

FIG. 7B is a perspective view schematically showing the second resinlayer being formed by transfer molding process.

FIG. 7C is a perspective view schematically showing the second resinlayer being formed by the transfer molding process.

FIG. 7D is a sectional view schematically showing a dicing process.

FIG. 8A is a sectional view showing an intermediate step in the processof second embodiment.

FIG. 8B is a sectional view showing a light emitting device of thesecond embodiment.

FIG. 9A is a sectional view showing an intermediate step in the processof third embodiment.

FIG. 9B is a sectional view showing a light emitting device of the thirdembodiment.

FIG. 10 is a perspective view showing an example of light emittingdevice according to fourth embodiment.

FIG. 11 is a sectional view taken along lines X-X of the light emittingdevice shown in FIG. 10.

FIG. 12 is a perspective view showing an example of the packageassembly.

FIG. 13 is a partially enlarged plan view showing a part of the packageassembly.

FIG. 14A is a sectional view showing a process of forming a sealingresin layer.

FIG. 14B is a sectional view showing a process that follows FIG. 14A.

FIG. 14C is a sectional view showing a process that follows FIG. 14B.

FIG. 14D is a sectional view showing a process that follows FIG. 14C.

FIG. 14E is a sectional view showing a process that follows FIG. 14D.

FIG. 14F is a sectional view showing a process that follows FIG. 14E.

FIG. 15 is a perspective view schematically showing the light emittingdevice shown in FIG. 10 mounted on a mounting substrate.

FIG. 16A is a graph showing light distribution characteristic of Example1 and Comparative Example 1 in direction of 0°.

FIG. 16B is a graph showing light distribution characteristic of Example1 and Comparative Example 1 in direction of 90°.

FIG. 17A is a sectional view showing a light emitting device (sample 1)of Example 2.

FIG. 17B is a sectional view showing a light emitting device (sample 2)of Example 2.

FIG. 17C is a sectional view showing a light emitting device (sample 3)of Example 2.

FIG. 18A is a graph showing light distribution characteristic of Example2 in direction of 0°.

FIG. 18B is a graph showing light distribution characteristic of Example2 in direction of 90°.

FIG. 19A is a graph showing light distribution characteristic of Example3 and Comparative Example 2 in direction of 0°.

FIG. 19B is a graph showing light distribution characteristic of Example3 and Comparative Example 2 in direction of 90°.

FIG. 20A is a graph showing the distribution of chromaticity coordinatex of Example 3 and Comparative Example 2 in direction of 0°.

FIG. 20B is a graph showing the distribution of chromaticity coordinatex of Example 3 and Comparative Example 2 in direction of 90°.

FIG. 21A is a graph showing the distribution of chromaticity coordinatey of Example 3 and Comparative Example 2 in direction of 0°.

FIG. 21B is a graph showing the distribution of chromaticity coordinatey of Example 3 and Comparative Example 2 in direction of 90°.

FIG. 22 is a sectional view showing the process of forming the sealingresin layer by transfer molding process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

AS shown in FIG. 1, the light emitting device according to thisembodiment comprises a substrate 2, a positive electrode 6 and anegative electrode 4 formed on the substrate 2, a light emitting diode 8connected to the positive electrode 6 and negative electrode 4,transparent resin layers (12 and 14) that cover the light emitting diode8, and a fluorescent material 16 that is dispersed in the transparentresin layers 12 and 14, wherein the fluorescent material 16 that isdispersed in the transparent resin layers 12 and 14 is excited with thelight emitted by the light emitting diode to emit light of a colordifferent from that of the light emitted by the light emitting diode 8.The transparent resin layers 12 and 14 that cover the light emittingdiode 8 consist of the first transparent resin layer 12 that includesthe fluorescent material 16 and the second transparent resin layer 14formed on the first transparent resin layer 12. The second transparentresin layer 14 is processed into a curved shape so as to constitute alens. The first transparent resin layer 12 and the second transparentresin layer 14 are cut so as to be substantially flush on a pair of sidefaces of the light emitting device 1 that oppose each other and thefirst transparent resin layer 12 is exposed.

The transparent resin layers 12 and 14 that cover the light emittingdiode 8 have such a two-layer constitution of the first transparentresin layer 12 and the second transparent resin layer 14 and the firsttransparent resin layer 12 includes the fluorescent material 16dispersed therein and the second transparent resin layer 14 has a lensformed therein, so that excellent light distribution characteristic isachieved. On the one hand, as the les is formed in the secondtransparent resin layer 14, desired light distribution characteristic isobtained according to the lens shape. On the other hand, as thefluorescent material 16 is dispersed in the first transparent resinlayer 12, it is disposed in the vicinity of the light emitting diode 8.As a result, function of the second transparent resin layer 14 as a lensis less likely to be affected by the diffusion of light by thefluorescent material 16, and color unevenness is less likely to beobserved in different directions of view.

The first transparent resin layer 12 and the second transparent resinlayer 14 are cut so as to be substantially flush on the side faces ofthe light emitting device 1 and the first transparent resin layer 12wherein the fluorescent material 16 is dispersed is exposed to theoutside. As a result, the devices can be made thinner than theconventional light emitting device that has a recess filled with theresin having the fluorescent material is dispersed therein, by an amountcorresponding to the thickness of the side wall of the recess.

Also because the side face 12 a of the first transparent resin layerthat includes the fluorescent material 16 is dispersed therein isexposed on the side face which adjoins the light emitting surface wherethe lens is formed, color tone can be corrected without substantiallyaffecting the lens characteristics. That is, the amount of thefluorescent material 16 can be changed by, for example, changing thethickness of the transparent resin layer wherein the fluorescentmaterial is dispersed by grinding the side face of the first transparentresin layer 12. This enables it to change the proportions of intensitiesof light emitted by the light emitting diode 8 and light emitted by thefluorescent material 16, thereby making it possible to correct the colortone. On the other hand, shape of the lens formed on the secondtransparent resin layer 14 undergoes no substantial change when thethickness of the transparent resin layer is changed by grinding the sideface of the first transparent resin layer 12. As a result, color tonecan be corrected without affecting the lens characteristics.

The constitution will now be described in more detail.

The light emitting device shown in FIG. 1 has the negative electrode 4and the positive electrode 6 formed with a predetermined distance fromeach other on the insulating substrate 2 having substantiallyrectangular parallelepiped shape having flat top surface. The negativeelectrode 4 and the positive electrode 6 are connected to mountingelectrodes (not shown) that are formed on the back surface of theinsulating substrate 2 via through holes (not shown). The light emittingdiode 8 having a pair of positive and negative electrodes formed on thesemiconductor surface side thereof is mounted on the negative electrode4 of the insulating substrate 2, while the negative electrode of thelight emitting diode is connected to the negative electrode 4 providedon the insulating substrate and the positive electrode of the lightemitting diode is connected to the positive electrode 6 provide on theinsulating substrate, by the wires 10. A semi-cylindrical firsttransparent resin layer 12 is formed so as to cover the light emittingdiode 8. Formed on the first transparent resin layer 12 is the secondtransparent resin layer 14 so as to cover substantially the entiresurface of the insulating substrate 2. The side face 2 a of theinsulating substrate, the side face 12 a of the first transparent resinlayer 12 and the side face 14 a of the second transparent resin layer 14are cut so as to be substantially flush, while the first transparentresin layer is exposed to the outside.

FIG. 2 is a sectional view taken along lines X-X′ of the light emittingdevice shown in FIG. 1. As shown in FIG. 2, the fluorescent material 16is dispersed in the first transparent resin layer 12. The fluorescentmaterial 16 is excited by light emitted by the light emitting diode 8and converts it to light of a longer wavelength. For example, in casethe light emitting diode 8 emits blue light, the fluorescent material 16may absorb a part of the blue light emitted and emit yellow light thathas a longer wavelength. The blue light emitted by the light emittingdiode 8 and the yellow light emitted by the fluorescent material areblended to produce white light. That is, the first transparent resinlayer 12 seals the light emitting diode while at the same timefunctioning as a wavelength converting layer that converts thewavelength of a part or all of the light emitted by the light emittingdiode.

The second transparent resin layer 14 is processed into a curved surfaceso as to form the top surface 14 b into a lens surface as shown in FIG.1 and FIG. 2. In the example shown in FIG. 1 and FIG. 2, asemi-cylindrical lens is formed in the top surface 14 b of the secondtransparent resin layer. The lens forming surface 14 b of the secondtransparent resin layer serves as the light emitting surface. Thecylindrical lens is not curved in the cross section along the shorteraxis of the light emitting device 1 so as to allow light to propagatestraight, but is curved in the cross section along the longer axis ofthe light emitting device 1 so as to bend light toward the normaldirection. As a result, light emitted by the light emitting diode 8and/or the fluorescent material 16 is bent toward the normal directionin the longitudinal direction of the light emitting device 1 whilepassing through the second transparent resin layer 14. Thus the secondtransparent resin layer 14 serves as a sealing layer for protecting thelight emitting diode 8 while at the same time functioning as a lens thatcontrols the direction of light emitted by the light emitting device. Inthis embodiment, the second transparent resin layer 14 does not have thefluorescent material 16 dispersed therein. Otherwise, the fluorescentmaterial 16 diffuses light and compromises the lens function of thesecond transparent resin layer 14. The second transparent resin layer 14may include such a small amount of the fluorescent material dispersedtherein that does not compromise the lens function of the secondtransparent resin layer 14. In this case, mean concentration of thefluorescent material included in the second transparent resin layer 14is preferably not higher than 1/10 and more preferably not higher than1/100 of the mean concentration of the fluorescent material included inthe first transparent resin layer.

FIG. 3 is a perspective view schematically showing the light emittingdevice 1 shown in FIG. 1 and FIG. 2 mounted on a substrate in the formof side view type light emitting device. The light emitting device 1 ismounted on the substrate 3 on the side face of the device parallel tothe longitudinal direction thereof as the mounting surface. At thistime, top surface 14 b of the second transparent resin layer 14 thatserves as the light emitting surface is substantially perpendicular tothe mounting substrate. Since the light emitting device 1 is formed sothat the insulating substrate 2, the first transparent resin layer 12and the second transparent resin layer 14 are all substantially flush onthe side face that makes contact with the mounting substrate 3, it haswide and flat mounting surface that enables stable mounting. Formed onthe surface of the mounting substrate 3 are positive and negative leadelectrodes 18 and 20, which are connected to the mounting electrodes(not shown) formed on the back surface of the insulating substrate ofthe light emitting device 1 by solder 22.

In the light emitting device of this embodiment, the transparent resinlayer that seals the light emitting diode 8 has two-layer structure ofthe first transparent resin layer 12 and the second transparent resinlayer 14, with the first transparent resin layer 12 including thefluorescent material 16 dispersed therein and the second transparentresin layer 14 having the lens formed therein. As a result, the lightemitting device functions as a side view type light emitting device thathas excellent optical effect. On the one hand, as the cylindrical lensis formed in top surface 14 b of the second transparent resin layer,light emitted by the light emitting device 1 is bent toward the normaldirection in the direction parallel to the mounting substrate surface,thus increasing the luminous intensity of light in the normal direction.On the other hand, as the second transparent resin layer 14 does notsubstantially include the fluorescent material 16 that diffuses lightdispersed therein, lens function thereof is not compromised, so thatlight is effectively bent in the normal direction. The secondtransparent resin layer 14 does not show the lens function in thedirection perpendicular to the mounting substrate. However, since lightpropagating in the direction perpendicular to the mounting substrate isblocked by the mounting substrate 3, it is relatively less important tocontrol the direction of light. Also because the fluorescent material 16is dispersed in the first transparent resin layer 12, it is disposed inthe vicinity of the light emitting diode 8. As a result, colorunevenness is less likely to be observed in different directions ofview, and it functions more like a point source.

In the light emitting device of this embodiment, the first transparentresin layer 12 and the second transparent resin layer 14 are cut so asto be substantially flush on the side face that adjoins the lightemitting surface 14 b where the lens is formed, and the side face 12 aof the first transparent resin layer wherein the fluorescent material isdispersed is exposed to the outside. As a result, the devices can bemade thinner than the conventional light emitting device that has arecess filled with the resin which includes the fluorescent material isdispersed therein, by an amount corresponding to the thickness of theside wall of the recess. Also color tone can be corrected withoutsubstantially affecting the lens characteristics. That is, the amount ofthe fluorescent material (not shown) in the first transparent resinlayer 12 a can be changed by changing the thickness W of the transparentresin layer to W′ by, for example, grinding the side face 12 a of thefirst transparent resin layer and the side face 14 a of the secondtransparent resin layer. This enables it to change the proportions ofintensities of light emitted by the light emitting diode 8 and lightemitted by the fluorescent material 16, thereby making it possible tocorrect the color tone. On the other hand, shape of the lens formed onthe top surface 14 b of the second transparent resin layer undergoes nosubstantial change when the thickness of the transparent resin layer Wis changed by grinding the side face 12 a of the first transparent resinlayer and the side face 14 a of the second transparent resin layer. As aresult, color tone can be corrected without affecting the lenscharacteristics.

In the light emitting device of this embodiment, since the firsttransparent resin layer 12 can be formed by either line applicationprocess or printing method as will be described later, there is also anadvantage that it can be manufactured easily.

Components of the light emitting device 1 will now be described indetail below.

(First Transparent Resin Layer 12)

The first transparent resin layer 12 is preferably formed in thevicinity of the light emitting diode 8 as far as possible. This isbecause the fluorescent material 16 that is dispersed in the firsttransparent resin layer 12 and emits light becomes proximate to an idealpoint light source when it is distributed within a small region. Morepreferably, the first transparent layer 12 is formed in contact with thesubstrate 2. This further improves the light scattering by fluorescentmaterial 16 and color-mixing effect. Also, a fixing strength of thefirst transparent resin layer 12 is improved. Height of the firsttransparent resin layer 12 is preferably as low as possible. However,when the height is lower than the wire 10, the wire 10 is stretched overthe first transparent resin layer 12 and the second transparent resinlayer 14, thus making the wire 10 susceptible to breakage. Therefore,height of the first transparent resin layer 12 is preferably beyond theheight of the wire 10. When the wire 10 has sufficient strength, thefirst transparent resin layer may cover a part of the wire as shown inFIG. 4. In order to mimic an ideal light source as far as possible, itis preferable to cause the fluorescent material 16 to sediment in thefirst transparent resin layer 12. However, degree of sedimentation ispreferably kept within a proper range, since excessive sedimentation ofthe fluorescent material 16 makes it difficult to correct the color toneby grinding the first transparent resin layer 12. It is preferable thatthe first transparent resin layer 12 has semi-cylindrical shape, and thecross section parallel to the mounting surface, namely the section thatis perpendicular to the light emitting surface, has semi-circular orsemi-oval cross section. This results in less variability in color withthe direction of observation. In order to form the first transparentresin layer 12 in the shape described above, it is preferable to employthe line application process described in this embodiment. The firsttransparent resin layer 12 may also be formed by printing as will bedescribed in the second embodiment.

There is no limitation to the kind of material that constitutes thefirst transparent resin layer 12, as long as it allows the light emittedby the light emitting diode and the light emitted by the fluorescentmaterial to transmit therethrough and allows the fluorescent material 16to be stably dispersed therein. For example, such resins as epoxy resin,silicone resin, hard silicone resin, modified silicone resin, urethaneresin, oxetane resin, acryl resin, polycarbonate resin or polyimideresin may be used. Besides a resin, glass may also be used. The firsttransparent resin layer 12 may also include a filler or a diffusionagent dispersed therein. Since the first transparent resin layer 12 issusceptible to the influence of the heat generated by the light emittingdiode 8, it is preferably formed from a resin that has sufficient heatresistance. For example, epoxy resin, silicone resin, hard siliconeresin, modified silicone resin, urethane resin or oxetane resin ispreferably used. More preferably, epoxy resin, silicone resin, modifiedsilicone resin, urethane resin or oxetane is used. Further morepreferably, epoxy resin, silicone resin, modified silicone resin oroxetane resin are used. Viscosity of the first transparent resin layeris preferably in a range from 100 to 2000 mPa·s before curing. Viscosityherein refers to a value measured by using a cone plate type rotaryviscosity meter at the normal temperature. The first transparent resinlayer preferably attains such a level of hardness that maintains theshape by curing for a duration of several minutes to several hours at acuring temperature of 80 to 180° C.

(Second Transparent Resin Layer 14)

The lens formed in the second transparent resin layer preferably has alarge lens diameter in the direction parallel to the mounting surface.This is because the necessity to control the light distributioncharacteristic is higher in the direction parallel to the mountingsurface than in the direction perpendicular to the mounting substrate.Since it is necessary to keep the thickness smaller in the directionperpendicular to the mounting surface, lens diameter is preferablysmaller in this direction. Radius of curvature of the lens is alsopreferably smaller in the direction perpendicular to the mountingsubstrate. This is because a lens having a large radius of curvature inthe direction perpendicular to the mounting surface is likely toexperience variation in the characteristics thereof when the side facesof the first and second transparent resin layers are ground for thepurpose of correcting the color tone. The lens formed in the secondtransparent resin layer may be, for example, a cylindrical lens that hasa large radius of curvature only in the direction parallel to themounting substrate. Cross section of the second transparent resin layer14 in the direction perpendicular to the mounting surface is notnecessarily perfectly flat, but may be somewhat curved.

There is no limitation to the kind of material that constitutes thesecond transparent resin layer 14, as long as it allows the lightemitted by the light emitting diode and the light emitted by thefluorescent material to transmit therethrough. For example, such resinsas epoxy resin, silicone resin, hard silicone resin, modified siliconeresin, urethane resin, oxetane resin, acryl resin, polycarbonate resinor polyimide resin may be used. Besides a resin, glass may also be used.The second transparent resin layer 14 may also include a filler or adiffusion agent dispersed therein. Since the second transparent resinlayer 14 also serves to protect the first transparent resin layer 12 andthe light emitting diode 8, it is preferably made of a material that isexcellent in bonding with the insulating substrate 2, in weatherabilityand in hardness, and is less likely to catch dust. For example, epoxyresin, silicone resin, hard silicone resin, modified silicone resin,urethane resin or oxetane resin is preferably used. More preferably,epoxy resin, silicone resin, modified silicone resin, urethane resin oroxetane resin is preferably used. Further more preferably, epoxy resin,silicone resin, modified silicone resin or oxetane resin is used.

(Insulating Substrate 2/Electrodes 4, 6)

There is no limitation to the material that constitutes the insulatingsubstrate 2 as long as sufficient mechanical strength and sufficientlevel of insulation are ensured. For example, BT resin or glass epoxymay be used. It may also be constitutes from a number of epoxy resinsheets laminated together. The negative electrode 4 and positiveelectrode 6 formed on the insulating substrate 2 are preferably formedfrom metal layers including Cu as the main component. The negative andpositive electrode 4, 6 may be formed from, for example, Cu/Ni/Ag.

(Light Emitting Diode 8/Fluorescent Material 16)

There is no limitation to the combination of the light emitting diode 8and the fluorescent material 16 as long as the fluorescent material 16can convert part or all of light emitted by the light emitting diode tolight of a different wavelength. As an example, a combination of thelight emitting diode 8 and the fluorescent material 16 suitable forconstituting a white light emitting device that is under the highestdemand at present will be described below.

Light Emitting Diode 8

As the light emitting diode suitable for constituting a white lightemitting device, nitride semiconductor (In_(X)Al_(Y)Ga_(1-X-Y)N, 0≦X,0≦Y, X+Y≦1) may be used. This light emitting diode has a light emittinglayer formed from In_(x)Ga_(1-x)N (0<x<1), and allows it to change thewavelength of emission in a range from about 365 nm to 650 nm byadjusting the proportions of components.

In order to emit white light, it is preferable to set the wavelength ofemission from the light emitting diode to not less than 400 nm and notlarger than 530 nm, more preferably not less than 420 nm and not largerthan 490 nm, in consideration of the complementary color relationshipwith the light emitted by the fluorescent material. An LED chip thatemits ultraviolet ray having wavelength shorter than 400 nm may also beused, provided that a proper kind of fluorescent material is selected.

Fluorescent Material 16

The fluorescent material may be a fluorescent material that absorbslight emitted by a semiconductor light emitting diode comprising anitride semiconductor as a light emitting layer and converts it to lightof a different wavelength. The fluorescent material is preferably atleast one selected from among nitride fluorescent materials andoxynitride fluorescent material that is mainly activated with lanthanoidelements such as Eu and Ce; alkaline earth halogen apatitie fluorescentmaterial that is mainly activated with lanthanoid elements such as Euand transition metal elements such as Mn; alkaline earth metalhalogen-borate fluorescent material; alkaline earth metal aluminatefluorescent material; rare earth element aluminate fluorescent materialthat is mainly activated with alkaline earth silicate, alkaline earthsulfide, alkaline earth thiogallate, alkaline earth silicon nitride,germanate, or lanthanoid elements such as Ce; and organic and organiccomplexes that are mainly activated with rare earth silicate orlanthanoid elements such as Eu. For example, the following fluorescentmaterials can be used but are not limited thereto.

Examples of the oxynitride fluorescent material that is mainly activatedwith lanthanoid elements such as Eu and Ce include M₂Si₅N₈:Eu (Mrepresents at least one element selected from among Sr, Ca, Ba, Mg andZn). It also includes, in addition to M₂Si₆N₈:Eu, MSi₇N₁₀:Eu,M_(1.8)Si₅O_(0.2)N₈:Eu and M_(0.9)Si₇O_(0.1)N₁₀:Eu (M represents atleast one element selected from among Sr, Ca, Ba, Mg and Zn).

Examples of the acid nitride fluorescent material that is mainlyactivated with lanthanoid elements such as Eu and Ce include MSi₂O₂N₂:Eu(M represents at least one element selected from among Sr, Ca, Ba, Mgand Zn).

Examples of the alkaline earth halogen apatite fluorescent material thatis mainly activated with lanthanoid elements such as E and transitionmetal elements such as Mn include M₅(PO₄)₃X:R (M represents at least oneelement selected from among Sr, Ca, Ba, Mg and Zn, X represents at leastone element selected from F, Cl, Br and I, and R represents at least oneelement selected from among Eu, Mn, Eu and Mn).

Examples of the alkaline earth metal halogen-borate fluorescent materialinclude M₂B₅O₉X:R (M represents at least one element selected from amongSr, Ca, Ba, Mg and Zn, X represents at least one element selected fromamong F, Cl, Br and I, and R represents at least one element selectedfrom among Eu, Mn, Eu and Mn).

Examples of the alkaline earth metal aluminate fluorescent materialinclude SrAl₂O₄:R, Sr₄Al₁₄O₂₅:R, CaAl₂O₄:R, BaMg₂Al₁₆O₂₇:R,BaMg₂Al₁₆O₁₂:R and BaMgAl₁₀O₁₇:R(R represents at least one elementselected from among Eu, Mn, Eu and Mn).

Examples of the alkaline earth sulfide fluorescent material includeLa₂O₂S:Eu, Y₂O₂S:Eu and Gd₂O₂S:Eu.

Examples of the rare earth aluminate fluorescent material that is mainlyactivated with lanthanoid elements such as Ce include YAG fluorescentmaterials represented by the formulas: Y₃Al₅O₁₂:Ce,(Y_(0.8)Gd_(0.2))₃Al₅O₁₂:Ce, Y₃(Al_(0.8)Ga_(0.2))₅O₁₂:Ce and(Y,Gd)₃(Al,Ga)₅O₁₂. It also includes Tb₃Al₅O₁₂:Ce and Lu₃Al₅O₁₂:Ce inwhich portion or all of Y is substituted with Tb or Lu.

Example of the other fluorescent material include ZnS:Eu, Zn₂GeO₄:Mn andMGa₂S₄:Eu (M represents at least one element selected from among Sr, Ca,Ba, Mg and Zn, and X represents at least one element selected from amongF, Cl, Br and I).

If necessary, the above fluorescent materials can contain at least oneelement selected from among Tb, Cu, Ag, Au, Cr, Nd, Dy, Co, Ni and Ti,in place of Eu, or in addition to Eu.

The Ca—Al—Si—O—N oxynitride glass fluorescent material is a fluorescentmaterial composed mainly of an oxynitride glass comprising 20 to 50 mol% of CaCO₃ based on CaO, 0 to 30 mol % of Al₂O₃, 25 to 60 mol % of SiO,5 to 50 mol % of AlN, 0.1 to 20 mol % of rare earth oxide or transitionmetal oxide, the total content of five components being 100 mol %. Inthe fluorescent material composed mainly of the oxynitride glass, thenitrogen content is preferably 15% by weight or less, and thefluorescent glass preferably contains, in addition to rare earth elementions, 0.1 to 10 mol % of other rare earth element ions in the form ofrare earth oxide as a coactivator.

It is possible to use a fluorescent material which is other than theabove fluorescent materials and has the same performances and effects asthose of the fluorescent materials.

(Method of Correcting Color Tone)

The method of correcting color tone according to this embodiment willnow be described. When correction of color tone is carried out on anumber of light emitting devices, it is preferably carried out in thefollowing procedure.

Step 1

In step 1, chromaticity value is measured on all of the light emittingdevices after the first and second transparent resin layers have beencured (measurement of initial chromaticity value).

Step 2

In step 2, the light emitting devices are classified into groups eachcorresponding to a particular range of differences between thechromaticity value measured in step 1 and a target chromaticity value(grouping process). While a larger number of groups are preferable forthe purpose of achieving smaller difference in chromaticity value aftercorrection, a proper number of groups is determined in consideration ofthe required range of chromaticity value (specification) and theefficiency of manufacture.

Step 3

Last, in step 3, side faces of the first and second transparent resinlayers are ground to an extent that is preset according to the deviationfrom the target chromaticity value (grinding process). In other words,the light emitting devices belonging to the same group are ground toremove the same amount of resin that is set specifically to the group.With this method of correction, since the devices belonging to the samegroup can be corrected to the same chromaticity value, chromaticity canbe adjusted efficiently and difference in chromaticity value can bereduced. Grinding is preferably carried out on the side face opposite tothe mounting surface, so that the mounting surface would not loseflatness.

Grinding can be carried out, for example, as follows. A plurality ofdevices are arranged on a grinding apparatus to be ground so as tocontrol the chromaticity to the target value. A grinding wheel havingdisk shape, for example, mounted at the tip of a rotary shaft is used asa grinding tool, so as to grind the first transparent resin layer 12 andthe second transparent resin layer 14 to an extent that is presetaccording to the deviation from the target chromaticity value. When agrinding wheel is provided for each of the plurality of light emittingdevices arranged on the grinding apparatus, the plurality of lightemitting device can be processed at the same time. At this time, aplurality of light emitting devices may be grouped according to theamount of removal and ground at the same time, or the individual lightemitting devices may be ground to achieve the target chromaticity valuewhile measuring the chromaticity with an optical sensor one by one (inthis case, too, it needs not to say that the plurality of light emittingdevices can be processed at the same time by controlling the amount ofremoval individually with the optical sensor and the grinder providedfor each light emitting device).

(Manufacturing Method)

A method for manufacturing the light emitting device according to thisembodiment will now be described below.

1. Package Assembly

In the method for manufacturing according to this embodiment, a packageassembly comprising a collection of a plurality of packages is useduntil the second transparent resin layer is hardened so that theplurality of light emitting device can be manufactured at the same. Inthis package assembly, regions for mounting the light emitting diodes 8are arranged in a matrix configuration on the insulating substrate 2having a large area (refer to FIG. 7A). The negative electrode 4 and thepositive electrode 6 corresponding to each of the light emitting diodes8 are formed so as to interpose the region for mounting the lightemitting diode 8. The negative electrode 4 and the positive electrode 6of the packages disposed in a same column are connected to each other.That is, the negative electrode 4 and the positive electrode 6 in thesame column each form a continuous electrode (refer to FIG. 5A). Theinsulating substrate 2 is constituted from a stack of resin havingthickness from 0.06 mm to 2.0 mm, and has a plurality of through holes(not shown) that penetrate the substrate in the direction of thickness.The negative electrode 4 and the positive electrode 6 are connected viathe through holes to the mounting electrodes formed on the back surfaceof the insulating substrate 2.

2. Mounting the Light Emitting Diode 8

The light emitting diode 8 are die-bonded at predetermined positions ofthe negative electrodes 4 of the package assembly constituted asdescribed above, and are connected in predetermined arrangement with thewires 10 (refer to FIG. 5A).

3. Formation of First Transparent Resin Layer 12

Then the first transparent resin layer 12 is formed. The firsttransparent resin layer 12 has a predetermined quantity of fluorescentmaterial 16 dispersed therein. The first transparent resin layer 12 ispreferably formed by the line application process shown in FIG. 5Athrough 5C. The line application process enables it to make the firsttransparent resin layer 12 thinner while making the manufacturingprocess simpler. Also because the line application process forms thefirst transparent resin layer 12 by making use of surface tension, thefirst transparent resin layer 12 can be formed along the negativeelectrode 4 and the positive electrode 6. The region where the firsttransparent resin layer 12 is formed can be restricted to the vicinityof the light emitting diode 8 by selecting a proper configuration of thenegative electrode 4 and the positive electrode 6.

According to the line application process, a dispenser 24 is moved alongthe arrangement of the light emitting diode 8 while discharging apredetermined amount of the first transparent resin from the dispenser24, thereby to form the resin layer continuously in a linearconfiguration as shown in FIG. 5A. When the line application process isemployed, configuration of the first transparent resin layer 12 can bedetermined according to the surface tension of the resin. For example,periphery of the positive electrode and the negative electrode islocated at a position higher by the thickness thereof than the surfaceof the insulating substrate 2. As a result, when the height differenceis large enough, the first transparent resin layer 12 is prevented bythe surface tension from flowing beyond the peripheries 4 a and 6 a ofthe negative electrode 4 and the positive electrode 6 as shown in FIGS.5B and 5C. The first transparent resin layer 12 can also be held bysurface tension at a height a little above the wire 10 when the amountof discharge is properly set. The first transparent resin layer 12 isformed to have a cross section of semi-circular or semi-oval shape asshown in FIG. 5C. Thus the line application process makes it possible toprocess a number of chips at the same time in a short period of timewith a very simple constitution, and also stabilizes the shape. As aresult, forming the first transparent resin layer 12 by the lineapplication process provides advantages of convenience in volumeproduction and less difference in color tone.

In case the first transparent resin layer has low surface tension, theshape may not be maintained by the height difference corresponding tothe thickness of the electrodes 4, 6 only. In this case, an arrangementto prevent the first transparent resin from flowing may be provided. Forexample, FIG. 6A shows a wall 32 formed from a resin or the like on theoutside of the negative electrode 4 and the positive electrode 6. FIG.6B shows a groove 34 formed on the outside of the negative electrode 4and the positive electrode 6. FIG. 6C shows a step 36 formed by raisingthe insulating substrate 2 on the outside of the negative electrode 4and the positive electrode 6.

The first transparent resin layer 12 that has been formed by the lineapplication process is then cured. If the first transparent resin is athermosetting resin, it may be applied by the line application processand then heated to harden. Sedimentation speed of the fluorescentmaterial 16 in the first transparent resin layer 12 can be controlled bymeans of the time interval from the end of line application process tothe start of curing and the viscosity of the transparent resin before orduring curing. The longer the time interval from the end of lineapplication process to the start of curing, the faster the sedimentationof the fluorescent material 16 in the first transparent resin layer 12.Also the lower the viscosity of the transparent resin 12 before curing,the faster the sedimentation of the fluorescent material 16 in the firsttransparent resin layer 12. Even when the transparent resin has highviscosity before curing, if it changes to lower viscosity when heated asin the case of epoxy, sedimentation of the fluorescent material 16 cantake place while the viscosity is low.

4. Formation of Second Transparent Resin Layer 14

Then the second transparent resin layer 14 is formed. To form the secondtransparent resin layer 14, such methods as transfer molding,compression molding and injection molding may be employed. Thedescription that follows will take transfer molding as an example.First, as shown in FIG. 7A, a package assembly 5 having the firsttransparent resin layer 12 formed thereon is prepared. Then as shown inFIG. 7B, the package assembly 5 is sandwiched by transfer molds 26 and28 from above and below. In the example shown in FIG. 7A, the lower mold26 is flat and the upper mold 28 has a lens forming cavity 28 a for thepurpose of forming the second transparent resin layer. Then as shown inFIG. 7C, the second transparent resin layer 14 is poured through a gateformed between the upper mold 28 and the package assembly 5. The secondtransparent resin layer 14 is prepared in the form of semi-moltenpellets and is melted while being pressed into the gate. After beingheated for a short period of time within the mold to harden, the resinis taken out of the molds and is heated further so as to form the secondtransparent resin layer 14. When the second transparent resin layer 14is formed by the transfer molding process, the resin is required to havea somewhat high level of viscosity. For example, epoxy resin is suitedto the transfer molding process.

Instead of the transfer molding process, compression molding process maybe used to form the second transparent resin layer 14. When a resin inliquid phase is used, in particular, it is preferable to employ thecompression molding process rather than the transfer molding process toform the second transparent resin layer 14. When the second transparentresin layer 14 is formed by the compression molding process, the secondtransparent resin applied over the entire surface of the packageassembly 5 is pressed by a compression mold from above, so as to beheated and harden.

5. Dicing

Then the light emitting devices are cut with predetermined width andpredetermined length out of the package assembly 5 by dicing in twodirections as shown in FIG. 7D, thereby to complete the light emittingdevice.

Second Embodiment

In this embodiment, an example of forming the first transparent resinlayer 12 by printing process will be described. The process is similarto that of the first embodiment with other respects.

First, as shown in FIG. 8A, the first transparent resin layer 12 isformed by printing over the entire surface of the package assembly 5.The first transparent resin layer 12 is formed over the entire surfaceof the insulating substrate 2, and is flat on the top surface. Thicknessof the first transparent resin layer 12 is kept large enough to behigher than the wire 10, so that the wire 10 does not bend or break whenthe first transparent resin layer 12 is printed. Then the firsttransparent resin layer 12 is heated to harden.

Then the second transparent resin layer 14 having the lens formedtherein is formed by a method similar to that of the first embodiment onthe first transparent resin layer 12 that has been formed over theentire surface of the insulating substrate 2. After hardening the secondtransparent resin layer 14, the light emitting device 1 is obtained asshown in FIG. 8B by dicing the package assembly in two directions. Thefirst transparent resin layer 12 formed by the method of this embodimenthas rectangular parallelepiped shape having substantially the same areaas the insulating substrate 2.

When the first transparent resin layer 12 is formed by printing as inthis embodiment, the first transparent resin layer 12 can be formed in ashorter period of time than in the case of employing the lineapplication process as in the first embodiment. However, since theprinting method requires it to position the top surface of the firsttransparent resin layer sufficiently higher than the wire 10, the firsttransparent resin layer 12 tends to become thicker than in the case ofthe line application process. Also because the fluorescent material 16is distributed over the entire surface of the insulating substrate 2 asshown in FIGS. 8A and 8B, color unevenness is likely to occur withdifferent directions of observation.

Third Embodiment

In the third embodiment, a method for suppressing the fluorescentmaterial 16 from spreading while forming the first transparent resinlayer by the printing method will be described.

First, as shown in FIG. 9A, before the first transparent resin layer 12is formed by printing, a mask 30 that limits the range of printing thefirst transparent resin layer 12 is formed on the insulating substrate30. The mask 30 is formed from, for example, a resist. The mask 30 maybe formed in parallel stripes that interpose the array of the lightemitting diode 8 from the right and left, so as to limit the range ofprinting the first transparent resin layer 12 within the vicinity of thelight emitting diode 8.

After hardening the first transparent resin layer 12, the mask 30 isremoved. Then the second transparent resin layer 14 is formed by amethod similar to that of the first embodiment. After hardening thesecond transparent resin layer 14, the light emitting device 1 isobtained as shown in FIG. 9B by dicing the package assembly in twodirections.

As shown in FIG. 9B, the first transparent resin layer 12 formed by themethod of this embodiment has substantially rectangular parallelepipedshape having a dimension in the longitudinal direction shorter than theinsulating substrate 2. Accordingly, the range of printing the firsttransparent resin layer 12 is limited within the vicinity of the lightemitting diode 8. As a result, color unevenness with differentdirections of observation is suppressed better than in the secondembodiment.

While an example of forming the first transparent resin layer 12 byprinting method has been described, the first transparent resin layer 12may also be formed by spraying or molding process.

Fourth Embodiment

In this embodiment, an aspect of the invention where the resin layer isformed in a single layer is described. The first through thirdembodiments require two processes; one to form the resin layer thatincludes the fluorescent material (fluorescent material impregnatedlayer) and one to form the lens-shaped resin layer that does not includethe fluorescent material (lens layer), in order to concentrate thefluorescent material near the light emitting diode.

In case the fluorescent material impregnated layer and the lens layerare formed in separate processes, the fluorescent material layer tendsto adsorb organic matter and moisture onto the surface thereof beforethe lens layer is formed. This results in the inclusion of foreignmatter such as organic matter and moisture in the region of the sealingresin layer near the light emitting diode, which makes the lightemitting diode and the fluorescent material more likely to deteriorate,thus leading to a shorter service life. Moreover, there is a possibilityof the moisture trapped in the interface between the fluorescentmaterial impregnated layer and the lens layer causes water vaporexplosion during solder reflow leading to peel off in the interface orlight emission failure.

In case the fluorescent material impregnated layer and the lens layerare formed from different materials, difference in the refractive indexin the interface may cause a decrease in the efficiency of lightemission. Even when the fluorescent material impregnated layer and lenslayer are formed from the same material, a slight difference in therefractive index may be generated in the interface as the lens layer isformed after the fluorescent material layer has been hardened on thesurface.

As shown in FIG. 10, the light emitting device of this embodimentcomprises the substrate 2, the positive electrode 6 and the negativeelectrode 4 formed on the substrate 2, the light emitting diode 8connected to the positive electrode 6 and negative electrode 4, asealing resin layer 40 that covers the light emitting diode 8, thefluorescent material 16 that absorbs at least part of light emitted bythe light emitting diode 8 and converts it to light of longerwavelength, and a lens that changes the direction of light emission fromthe light emitting diode 8 and/or the fluorescent material 16. Thesealing resin layer 40 includes the fluorescent material 16 and isformed integrally so as to constitute the lens. The fluorescent material16 is distributed with a higher concentration in a region near thesurface of the light emitting diode 8 than in a region near the surfaceof the sealing resin layer 40.

The light emitting device of this embodiment is characterized in thatthe sealing resin layer 40 that includes the fluorescent material 16dispersed therein constitutes the lens for controlling the lightdistribution, and that the fluorescent material 16 included in thesealing resin layer 40 is concentrated in the vicinity of the lightemitting diode 8. This makes it possible to have the dispersion of thefluorescent material 16 in the vicinity of the light emitting diode 8and the formation of the lens for controlling the light distribution ofthe light emitting device 1 carried out in a single process. Alsobecause the sealing resin layer 40 of the light emitting diode 8 isformed in a single operation without hardening amid the course, it isless likely that moisture or organic matter enters the sealing resinlayer 40. Moreover, since there is no discontinuity in refractive indexbetween the light emitting diode and the fluorescent material,extraction of light with higher efficiency is made possible.

The sealing resin layer 40 having the fluorescent material dispersedtherein is preferably formed into the lens shape by compression moldingprocess. Since the sealing resin layer 40 that has been applieduniformly can be hardened while applying a pressure with a mold in thecompression molding process, a desired lens can be formed by using athermosetting resin that has low viscosity of 5000 mPa·s at the normaltemperature before hardening, particularly from 300 mPa·s to 2000 mPa·s,or a thermosetting resin of which viscosity once decreases and thenincreases again as the temperature rises. Use of a thermosetting resinhaving low initial level of viscosity or a thermosetting resin of whichviscosity once decreases during curing makes it possible to causesedimentation of the fluorescent material included in the sealing resinlayer before or during curing, and cause the fluorescent material to beconcentrated in the vicinity of the light emitting diode. Also becausethe lens shape is determined by the mold, the lens of a desired diameterand radius of curvature can be formed. To summarize, placement of thefluorescent material in the vicinity of the light emitting diode andformation of the lens having the desired characteristics can be carriedout at the same time by the single operation of forming the sealingresin layer.

In the prior art, contrary to the above, placement of the fluorescentmaterial in the vicinity of the light emitting diode and formation ofthe lens having the desired characteristics are not carried out at thesame time, and it is difficult to do so. For example, JapaneseUnexamined Patent Publication No. 2000-196000 and Japanese UnexaminedPatent Publication No. 2001-352105 disclose methods of forming thesealing resin layer in lens shape by the transfer molding process.Formation of lens shape by the transfer molding process is carried out,for example, as follows. First, as shown in FIG. 22, the substrate 2carrying the light emitting diode 8 mounted on the top surface thereofis sandwiched by transfer molds 26 and 28 from above and below. Then asshown in FIG. 22, the thermosetting resin 40 is poured through a gate 28a formed between the upper mold 28 and the substrate 2. Thethermosetting resin to be poured is prepared in the form of tablets andis turned semi-molten by induction heating and is charged into a pot 28b of the mold. The molds 26 and 28 are heated to a high temperature ofabout 170° C., and the resin 40 that has been charged starts melting atthe instant it touches the mold. The resin is pressurized by a plunger20 from above the pot so as to enter a cavity that is disposed betweenthe mold 26 and the substrate 2. Since the resin 40 is caused to flowinto the cavity at a relatively low speed, the wire 10 or the like isless likely to be damaged. In this case, resin stream within the moldcannot be controlled, thus resulting in higher possibility of voids orother defects to occur, unless the sealing resin layer has somewhat highlevel of viscosity. This results in such a situation as the fluorescentmaterial dispersed in the sealing resin layer, which is to be formedinto the lens, hardly undergoes sedimentation in the sealing resin layerthat has been poured into the mold. As a result, although the desiredlens shape can be formed in the mold, the fluorescent material isdistributed throughout the sealing resin layer, thus causing colorunevenness with different directions of observation.

In case the sealing resin layer having low viscosity is dripped onto thelight emitting diode and hardened as described in Japanese UnexaminedPatent Publication No. 2000-315824, sedimentation of the fluorescentmaterial occurs in the sealing resin layer and therefore the fluorescentmaterial can be placed in the vicinity of the light emitting diode. Inaddition, surface of the sealing resin layer can be formed in the shapeof lens to some extent due to the surface tension of the sealing resinlayer before being hardened. However, since the shape of the lens to beformed is determined by the surface tension of the sealing resin layer,it is difficult to form the lens that sufficiently controls the lightdistribution. That is, since it is impossible to freely control the lensshape, it is impossible to achieve the desired light distributioncharacteristic such as increasing the luminous intensity in the normaldirection or increasing the luminous intensity in an oblique direction.Also because the lens shape is determined by the surface tension andgravity, a drop of the sealing resin layer that has been drippedflattens when it has a large diameter, resulting in a large radius ofcurvature in the vicinity of the optical axis.

The sealing resin layer 40 in this embodiment is preferably formed froma thermosetting resin of which viscosity once decreases and thenincreases again as the temperature rises, or a thermosetting resin thathas low viscosity of 5000 mPa·s at the normal temperature beforehardening, particularly from 300 mPa·s to 2000 mPa·s. Even when a resinthat has viscosity of 5000 mPa·s or higher at the normal temperature maybe used provided that it allows sedimentation of the fluorescentmaterial when it is left for a sufficiently long period of time beforebeing cured in the mold. This enables sedimentation of the fluorescentmaterial to take place in the vicinity of the light emitting diode 8during or before the curing of the sealing resin layer 40. For thethermosetting resin of which viscosity once decreases and then increasesagain as the temperature rises, epoxy resin, silicone resin, hardsilicone resin, modified silicone resin, urethane resin, oxetane resin,acryl resin, polycarbonate resin or polyimide resin or the like may beused. More preferably, epoxy resin, silicone resin, hard silicone resin,modified silicone resin, urethane resin, oxetane resin is used. Furthermore preferably, hard silicone resin, epoxy resin or modified resin isused.

Concentration of the fluorescent material 16 in the vicinity of thesurface of the light emitting diode 8 is preferably not lower than 20times, more preferably not lower than 50 times the concentration of thefluorescent material in the vicinity of the surface of the sealing resinlayer 40. This causes the light emitting diode to emit light like apoint light source, thus reducing the color unevenness with differentdirections of observation. It is preferable that the fluorescentmaterial is not substantially included in the portion of the sealingresin layer 40 that is formed into lens. Since the fluorescent material16 used in common has refractive index different from that of thesurrounding sealing resin layer 40, it has an effect of diffusing thelight emitted by the light emitting diode 8 and other part of thefluorescent material 16. Thus when the portion of the sealing resinlayer 40 formed in lens shape includes the fluorescent material 16, lensfunction is hampered and desired light distribution characteristicbecomes difficult to achieve. The portion of the sealing resin layer 40that is formed in lens shape means a region that includes the opticalaxis of the lens and is interposed between a straight line connectingboth ends of the lens and the surface of the sealing resin layer 40 whenviewed from a section where the lens has the largest radius ofcurvature. The phrase “do not substantially include the fluorescentmaterial 16” means not only a situation in which the portion in questionincludes no fluorescent material at all but also a case where theintensity of light emitted by the fluorescent material included in thatportion is negligibly low compared to that of light emitted by the lightemitting diode or light emitted by the fluorescent material disposed inthe vicinity of the light emitting diode.

Compression molding process enables it to form the lens in any desiredshape in the sealing resin layer 40. The lens formed in the sealingresin layer 40 is preferably a lens that has different radii ofcurvature depending on the direction of light emission. This means tochange the radius of curvature with the direction of different sectionsof the lens. By forming the lens with different radii of curvaturedepending on the direction of light emission, it is made possible toachieve desired light distribution characteristic. Particularlyaccording to this embodiment, this effect is combined with that of thequasi point source construction realized by concentrating thefluorescent material in the vicinity of the light emitting diode, thusachieving excellent optical characteristics.

For example, a lens having radius of curvature of different values inthe horizontal direction and vertical direction can be formed. Anexample of lens having radius of curvature of different values in thehorizontal direction and vertical direction is a semi-cylindrical lens.When a semi-cylindrical lens is formed in the sealing resin layer 40, alight emitting device having excellent side view performance can bemade. Specifically, as the semi-cylindrical lens is formed in thesealing resin layer 40 and the side face of the semi-cylindrical lens isused as the mounting surface, the light emitting device of low profilecan be made and the mounting surface becomes wider as well thus enablingstable mounting. Since light emitted in the direction perpendicular tothe mounting substrate is blocked by the mounting substrate in the sideview type, it is important to control the emission in the directionparallel to the substrate, but the semi-cylindrical configuration of thelens provides lens characteristic in the direction parallel to thesubstrate similar to that of regular spherical lens. It also makes itpossible to correct the color tone without affecting the lenscharacteristics. That is, when thickness of the sealing resin layer ischanged by grinding the side face of the sealing resin layer 40,quantity of the fluorescent material included in the sealing resin layer40 can also be changed, thereby correcting the color tone. Since theshape of the lens formed on the top surface of the sealing resin layer40 does not change when the thickness of the resin layer is changed bygrinding the sealing resin layer 40, there is no substantial influenceon the lens characteristic.

The sealing resin layer 40 may also have a semi-spherical lens formedtherein having the same radius of curvature in all sections. When asemi-spherical lens is formed in the sealing resin layer 40, a lightemitting device having excellent top view performance can be made wherelight is extracted from the surface parallel to the mounting surface.

The light emitting device of this embodiment will now be described inmore detail.

FIG. 10 is a perspective view showing the light emitting deviceaccording to the fourth embodiment. FIG. 11 is a sectional view takenalong lines X-X′ of the light emitting device shown in FIG. 10. Thenegative electrode 4 and the positive electrode 6 are formed with apredetermined distance from each other on the insulating substrate 2 ofsubstantially rectangular parallelepiped shape that has flat topsurface. The negative electrode 4 and the positive electrode 6 areconnected to the mounting electrodes (not shown) that are formed on theback surface of the insulating substrate 2 via through holes (notshown). The light emitting diode 8 having a pair of positive andnegative electrodes formed on the semiconductor surface side is mountedon the negative electrode 4 of the insulating substrate 2, while thenegative electrode of the light emitting diode 8 is connected to thenegative electrode 4 of the insulating substrate and the positiveelectrode of the light emitting diode is connected to the positiveelectrode 6 provided on the insulating substrate, by the wires 10.

The semi-cylindrical and transparent sealing resin layer 40 is formed soas to cover the light emitting diode 8. The sealing resin layer 40includes the fluorescent material 16 that absorbs part of light emittedby the light emitting diode 8 and converts it to light of a longerwavelength dispersed therein. The fluorescent material 16 is excited bythe light emitted by the light emitting diode 8 and converts it to lightof a wavelength longer than that of the light emitting diode 8. When thelight emitting diode 8 emits blue light, for example, the fluorescentmaterial 16 may absorb a part of the blue light and emit yellow lightthat has a longer wavelength. The blue light emitted by the lightemitting diode 8 and the yellow light emitted by the fluorescentmaterial are blended to produce white light. The fluorescent material 16is precipitated in a lower part of the sealing resin layer 40 and isdistributed near the top surface of the insulating substrate 2 whereonthe light emitting diode 8 is mounted. As a result, quantity of thefluorescent material is suppressed from varying in different directionsof observation, thus mitigating the color unevenness with differentdirections of observation. Also distribution of the fluorescent material16 near the light emitting diode 8 makes the device having performancenear that of ideal point light source. The side face 2 a of theinsulating substrate and the side face 40 a of the sealing resin layer14 are cut so as to be substantially flush, and the fluorescent material16 is distributed up to the exposed side face 40 a.

The sealing resin layer 40 having semi-cylindrical configurationconstitutes a cylindrical lens, and serves to direct the light emittedby the light emitting diode 8 and light emitted by the fluorescentmaterial 16 in a desired direction. The sealing resin layer 40 has, forexample, semi-cylindrical configuration and has a large difference inrefractive index from the air that is in contact therewith. As a result,light emitted by the light emitting diode 8 and light emitted by thefluorescent material 16 are refracted in the surface of the sealingresin layer 40, and are directed in the desired direction. The lensconstituted by the sealing resin layer 40 is not limited to cylindricallens, and may have any shape as long as it has the desired lightcollecting capability and light diffusing capability. Diffusion of lightherein does not mean the diffusion by scattering of light, but meansspreading of light in a wider angle which may be provided by variousconvex lenses or concave lenses.

The light emitting device 1 of this embodiment is characterized in thatthe sealing resin layer 40 that includes the fluorescent material 16dispersed therein constitutes the lens for controlling the lightdistribution, and that the fluorescent material 16 included in thesealing resin layer 40 is concentrated in the vicinity of the lightemitting diode 8. This makes it possible to have the dispersion of thefluorescent material 16 in the vicinity of the light emitting diode 8and the formation of the lens for controlling the light distribution ofthe light emitting device 1 carried out in a single process. Alsobecause the sealing resin layer 40 of the light emitting diode 8 isformed in a single operation without hardening amid the course, it isless likely that moisture or organic matter enters the sealing resinlayer. Moreover, since there is no discontinuity in refractive indexbetween the light emitting diode 8 and the fluorescent material 16,extraction of light with high efficiency is made possible.

The light emitting device 1 of this embodiment can be manufactured byforming the sealing resin layer 40 having the fluorescent material 16dispersed therein into lens shape by the compression molding process.Since the sealing resin layer 40 that has been applied uniformly ishardened while applying a pressure with a mold in the compressionmolding process, a desired lens can be formed by using a thermosettingresin that has low viscosity of 5000 mPa·s or lower before hardening, ora thermosetting resin of which viscosity once decreases and thenincreases again as the temperature rises. Use of a thermosetting resinthat has low initial level of viscosity or a thermosetting resin ofwhich viscosity once decreases during curing makes it possible to causesedimentation of the fluorescent material 16 to take place in thesealing resin layer 40 before or during curing, and have the fluorescentmaterial 16 concentrated in the vicinity of the light emitting diode 8.Also because the lens shape is determined by the mold, the lens of adesired diameter and radius of curvature can be formed. To summarize,placement of the fluorescent material 16 in the vicinity of the lightemitting diode 8 and formation of the lens having the desiredcharacteristics can be carried out at the same time by the singleoperation of forming the sealing resin layer 40.

(Method for Manufacturing the Light Emitting Device 1)

A method for manufacturing the light emitting device 1 by thecompression molding process will now be described in detail below.

1. Preparation of Package Assembly

In this embodiment, too, the package assembly comprising a collection ofa plurality of light emitting device is used until the sealing resinlayer is hardened, similarly to the first embodiment. In this packageassembly 5, regions for mounting the light emitting diode 8 are arrangedin a matrix configuration on the insulating substrate 2 having a largearea as shown in FIG. 12. The negative electrode 4 and the positiveelectrode 6 are formed so as to interpose the region for mounting thelight emitting diode 8 from both sides as shown in FIG. 13. The lightemitting diode 8 is die-bonded on each negative electrode 4, while thenegative electrode 4 and the positive electrode 6 are connected to thelight emitting diode 8 with the wires 10. A set of the light emittingdiode 8, the negative electrode 4 and the positive electrode 6constitute one package. The negative electrode 4 and the positiveelectrode 6 of the packages disposed in a same column are connected toeach other. That is, the negative electrode 4 and the positive electrode6 in the same column each form a continuous electrode.

2. Application of Sealing Resin Layer 40 Including Fluorescent Material16

Then as shown in FIG. 14A, the package assembly 5 is placed on a lowermold 42 that has been heated to a predetermined temperature. The lowermold 42 is preferably heated to the primary curing temperature of thesealing resin layer 40 to be applied, in advance. Then as shown in FIG.14B, an appropriate amount of the thermosetting resin in liquid phasewith the fluorescent material 16 uniformly mixed therein is applied overthe top surface of the package assembly 5 by means of a dispenser 24 orthe like. This causes the sealing resin layer 40 with the fluorescentmaterial 16 uniformly mixed therein having a uniform thickness to coverthe light emitting diode 8, the negative electrode 4 and the positiveelectrode 6. The quantity of the sealing resin layer 40 applied is suchthat is enough to form the desired lens when compressed with the mold.It is preferable to form the layer to such a thickness as the wire 10 iscompletely embedded.

3. Formation and Primary Curing of Sealing Resin Layer 40

The sealing resin layer 40 is compressed with a predetermined pressureby placing an upper mold 44 on the sealing resin layer 40 that has beenapplied as shown in FIGS. 14C and 14D. The upper mold 44 has a cavity ofsemi-cylindrical lens shape. Primary curing of the sealing resin layer40 formed from the thermosetting resin is carried out by keeping it inthe state of being compressed by the upper mold 44 for a predeterminedperiod of time. The sealing resin layer 40 is preferably formed from athermosetting resin of which viscosity once decreases and then increasesagain as the temperature rises. For example, hard silicone resin, epoxyresin or the like may be used. This allows sedimentation of thefluorescent material 16 to take place in the sealing resin layer 40while the sealing resin layer 40 is heated in the molds 42 and 44 asshown in FIG. 14E. Temperature and duration of heating in the molds 42and 44 are set so that sufficient sedimentation of the fluorescentmaterial 16 occurs and the sealing resin layer 40 attains sufficienthardness that maintains the predetermined shape. For example,temperature of primary curing is preferably set in a range from 100 to170° C., more preferably from about 120 to 150° C. Duration of hardeningis preferably set in a range from 200 to 900 seconds and more preferablyfrom 250 to 600 seconds.

Forming the sealing resin layer 40 from the thermosetting resin of whichviscosity once decreases and then increases again as the temperaturerises has the following advantage. Since the sealing resin layer 40 hasa certain level of viscosity before being applied to the packageassembly 5, sedimentation of the fluorescent material 16 does notproceed much in the sealing resin layer 40 and therefore it is easy tomaintain the state of uniform dispersion of the fluorescent material. Asa result, the amount of the fluorescent material that is applied can besuppressed from varying among individual light emitting diode 8 when thesealing resin layer 40 having the fluorescent material dispersed thereinis applied to the package assembly 5. After the sealing resin layer 40has been applied to the light emitting diode 8, since the viscosity ofthe sealing resin layer 40 decreases as the temperature rises, thefluorescent material 16 precipitates to near the light emitting diode 8.For this reason, it is preferable to use a thermosetting resin of whichviscosity once decreases and then increases again as the temperaturerises, or a thermosetting resin that has low viscosity of 5000 mPa·s atthe normal temperature before hardening, particularly from 300 mPa·s to2000 mPa·s. Even when a resin that has viscosity of 5000 mPa·s or higherat the normal temperature may be used, provided that it allowssedimentation of the fluorescent material to take place when it is leftfor a sufficiently long period of time before being cured in the mold.

A thermosetting resin of which viscosity is low at the initial stage,and increases monotonously as the temperature rises may also be used. Inthis case, it is preferable that the resin is sufficiently stirred inthe dispenser 24 in order to prevent the fluorescent material fromprecipitating before application. In order to allow sufficientsedimentation of the fluorescent material after the application, it ispreferable to apply the sealing resin layer 40 before heating the molds42 and 44. For example, the sealing resin layer 40 may be applied beforeplacing the package assembly in the mold, and the package assembly maybe set in the mold after the fluorescent material 16 has sedimented.

4. Secondary Curing of Sealing Resin Layer 40

Then the package assembly 5 whereon the sealing resin layer 40 has beensubjected to primary curing is taken out of the mold, and the sealingresin layer 40 is subjected to secondary curing by heating underpredetermined conditions. The conditions of secondary curing arepreferably set so that the sealing resin layer 40 is completelyhardened. For example, it is preferable to set the temperature ofsecondary curing equal to or higher than that of the primary curing, andduration of secondary curing longer than that of the primary curing.When epoxy resin or hard silicone resin is used, it is preferable to setthe duration of secondary curing in a range from 3 to 5 hours, morepreferably 3.5 to 4.5 hours. When the secondary curing is carried outunder such conditions, such a problem can be prevented as unreactedhardener component remains in the sealing resin layer 40 and adverselyaffects the reliability of the light emitting diode 8. Throughout of theprocess can be improved by applying the secondary curing after takingout the package assembly from the molds 42 and 44.

5. Dicing

Then the package assembly 12 is cut to predetermined width andpredetermined length by dicing in two directions as shown in FIG. 14F,thereby to complete the light emitting device. Dicing is first carriedout in the direction parallel to the lens, so as to cut out a row ofpackage assembly 5 where the semi-cylindrical lenses are formed. Thepackage assembly of each row that has been cut out is then subjected todicing in the direction perpendicular to the longitudinal direction, soas to produce the individual light emitting devices 1.

According to this embodiment, as described above, placement of thefluorescent material 16 in the vicinity of the light emitting diode andformation of the lens having the desired characteristics can be carriedout at the same time by the single operation of forming the sealingresin layer 40. By using a thermosetting resin that has low initiallevel of viscosity or a thermosetting resin of which viscosity oncedecreases during curing, it is made possible to cause sedimentation ofthe fluorescent material 16 to take place in the sealing resin layer 40before or during curing, and have the fluorescent material 16concentrated in the vicinity of the light emitting diode 8. Such athermosetting resin may also be used that can be maintained in a lowviscosity state for a period of time long enough to allow thefluorescent material to precipitate in the mold. Also the lens of adesired diameter and radius of curvature can be formed by means of themolds 42 and 44.

When the lens is formed from the sealing resin layer 40 including thefluorescent material 16 dispersed therein by the compression moldingprocess as in this embodiment, it becomes unnecessary to use a cup forholding the resin that includes the fluorescent material as described inthe patent document 3. As a result, the sealing resin layer 40 thatincludes the fluorescent material 16 and has the lens formed therein canbe formed directly on the substantially flat top surface of theinsulating substrate 2. This makes it possible to extract light that isemitted by the light emitting diode 8 in the lateral direction withoutblocking. The present invention does not preclude an arrangement ofproviding a cup that accommodates the light emitting diode 8. When thelight emitted by the light emitting diode 8 and light emitted by thefluorescent material 16 are directed in the normal direction, inparticular, a cup may be provided as a reflector.

A light emitting device that has a configuration suited for side viewoperation can be easily manufactured by forming the lens ofsemi-cylindrical shape in the sealing resin layer 40 and dividing theindividual light emitting device by dicing as in this embodiment.

(Mounting and Color Correction of Light Emitting Device 1)

The processes of mounting the light emitting device and correcting thecolor according to this embodiment will now be described.

For the light emitting device of this embodiment, too, mounting andcolor correction can be carried out similarly to the first embodiment(refer to FIG. 15). The light emitting device 1 having semi-cylindricalshape can be mounted on the mounting substrate 3 using the flat surfaceof the half cylinder as the mounting surface. At this time, the topsurface 40 b of the sealing resin layer from which light is extracted isdisposed substantially perpendicular to the mounting substrate 3.

This light emitting device has the top and the bottom cut into flatsurfaces and therefore has profile lower than that of the light emittingdevice of the prior art. In addition, since the mounting surface isconstituted from the sealing resin layer and the substrate, the mountingsurface has a wider area that enables stable mounting.

Also because the cylindrical lens (cylindrical lens having convexsurface on one side) is formed on the top surface 40 b of the sealingresin layer, and the fluorescent material 16 included in the sealingresin layer 40 is concentrated in the vicinity of the light emittingdiode 8, excellent optical effect is achieved. That is, on the firstplace, since the cylindrical lens is formed on the top surface 40 b ofthe sealing resin layer, light emitted by the light emitting device 1 isbent in the direction parallel to the mounting substrate surface so asto propagate in the normal direction, thus resulting in higher luminousintensity in the normal direction. Also because the fluorescent material16 that diffuses light is precipitated in the sealing resin layer 40into the vicinity of the light emitting diode 8, lens functions of thesealing resin layer 40 is not hampered so that light is efficiently bentinto the normal direction. Also because the fluorescent material 16 isconcentrated near the light emitting diode 8, it works more like a pointlight source with less color unevenness with different directions ofobservation. While the sealing resin layer 40 does not exert the lensfunction in perpendicular to the mounting substrate, light propagatingin the direction perpendicular to the mounting substrate is blocked bythe mounting substrate 3 and therefore the absence of lens effect doesnot pose a significant problem.

Also color tone of the light emitting device according to thisembodiment can be controlled similarly to the first embodiment. That is,a shown in FIG. 15, the quantity of the fluorescent material included inthe sealing resin layer 40 can be changed by changing the thickness W ofthe sealing resin layer to W′ by grinding the side face 40 a of thesealing resin layer. This enables it to change the proportions ofintensities of light emitted by the light emitting diode 8 and thefluorescent material 16, thereby making it possible to correct the colortone. On the other hand, shape of the lens formed on the top surface 40b of the sealing resin layer undergoes no substantial change when thethickness W of the sealing resin layer is changed by grinding. As aresult, color tone can be corrected without affecting the lenscharacteristics.

When color tone is corrected for a number of light emitting devices atthe same time, it is preferable to employ the method described in thefirst embodiment.

The sealing resin layer 40 will now be described in detail. Theconstitution is similar to that of the first embodiment with otherrespects.

There is no limitation to the kind of material that constitutes thesealing resin layer 40, as long as it allows the light emitted by thelight emitting diode 8 and the light emitted by the fluorescent material16 to transmit therethrough and allows the fluorescent material 16 to bestably dispersed therein. In order to concentrate the fluorescentmaterial in the vicinity of the light emitting diode, however, it ispreferable to use a thermosetting resin of which viscosity oncedecreases and then increases again as the temperature rises, or athermosetting resin that has low viscosity of 5000 mPa·s or lower at thenormal temperature before hardening, particularly from 300 mPa·s to 2000mPa·s. This enables sedimentation of the fluorescent material 16 to takeplace in the vicinity of the light emitting diode 8 during or before thecuring of the sealing resin layer 40. For the thermosetting resin ofwhich viscosity once decreases and then increases again as thetemperature rises, hard silicone resin, epoxy resin or the like may beused. For thermosetting resin that has low viscosity of 5000 mPa·s orlower at the normal temperature before hardening, particularly from 300mPa·s to 2000 mPa·s, hard silicone resin, epoxy resin or the like may beused.

The lens formed in the sealing resin layer 40 is not limited tosemi-cylindrical lens described in this embodiment, and can be formed invarious shapes. For example, a semi-spherical lens that is convex on oneside is preferable for a top view type light emitting device where lightis extracted from a surface parallel to the mounting surface. Also alens other than convex configuration may also be employed depending onthe application. With any lens shape, it is necessary that the radius ofcurvature and the lens diameter are such that ensure the desired lightdistribution characteristic.

When a lens of substantially semi-cylindrical shape is formed for sideview application, radius of curvature may be provided in the directionperpendicular to the mounting surface as well in the direction parallelto the mounting surface. However, radius of curvature in the directionperpendicular to the mounting surface is preferably very small. This isbecause a lens having a large radius of curvature in the directionperpendicular to the mounting surface is susceptible to alteration ofthe lens characteristics when the side face of the sealing resin layeris ground to correct the color tone. In addition, it is not necessary toprovide a lens having a large radius of curvature in the directionperpendicular to the mounting substrate since light propagating in thedirection perpendicular to the mounting surface is blocked by themounting substrate.

It is necessary that the fluorescent material 16 dispersed in thesealing resin layer 40 is distributed with a higher concentration in aregion near the surface of the light emitting diode 8 than in a regionnear the surface of the sealing resin layer 40. Concentration of thefluorescent material in the region near the surface of the lightemitting diode 8 is preferably not less than 20 times, more preferably50 times that in the region near the surface of the sealing resin layer40. This enables it to suppress the quantity of the fluorescent materialfrom varying in different directions of observing the light emittingdiode 8, thus mitigating the color unevenness with different directionsof observation. Also distribution of the fluorescent material 16 nearthe light emitting diode 8 makes the device having performance near thatof ideal point light source. It is preferable that concentration of thefluorescent material in the region near the surface of the lightemitting diode 8 is not less than 100 times that in the region near thesurface of the sealing resin layer 40. This enables it to achieve lightdistribution characteristic approximate to that of a point light sourceand prevent color unevenness from occurring. More uniform diffusion oflight can be achieved by including a diffusion agent or the like in thesealing resin layer 40 near the surface thereof. Concentration of thefluorescent material in the region near the surface of the sealing resinlayer 40 means mean concentration (number of particles in unit volume)of the fluorescent material particles in a portion about 10% in lengthof the sealing resin layer 40 along the optical axis of the lens that isformed in the sealing resin layer 40. The concentration of thefluorescent material 16 in the region near the surface of the lightemitting diode 8 means mean concentration of the fluorescent materialparticles in a portion about 10% from the surface of the light emittingdiode 8 in the sealing resin layer 40 along the optical axis of thelight emitting diode.

It is preferable that the fluorescent material 16 does not substantiallyexist in the portion of the sealing resin layer 40 where the lens isformed. The fluorescent material 16 not only absorbs part of lightemitted by the light emitting diode 8 and converts it to a differentwavelength but also reflects and diffuses light emitted by the lightemitting diode 8 and by the other portion of the fluorescent material16. Consequently, fluorescent material existing in the portion of thesealing resin layer where the lens is formed hampers the lens functionand makes it difficult to achieve the desired light distributioncharacteristic. The portion of the sealing resin layer where the lens isformed refers to a region that includes the optical axis of the lens andis interposed between a straight line connecting both ends of the lensand the surface of the sealing resin layer when viewed from a sectionwhere the lens has the largest radius of curvature.

The first through fourth embodiments exemplify the cases where the lightemitting diode 8 emits light from the electrode side while theelectrodes of the light emitting diode 8 and the electrodes provided onthe insulating substrate 2 are connected by wire bonding. However, thepresent invention is not limited to this constitution, and the lightemitting diode 8 may also be mounted on the insulating substrate 2 byflip-chip bonding. Specifically, the light emitting diode is placed sothat the p-side electrode and the n-side electrode of the light emittingdiode oppose the positive and negative electrodes formed on theinsulating substrate 2, respectively, and the electrode that oppose eachother are connected together by an electrically conductive adhesivemember such as solder.

The light emitting diode to be mounted by flip-chip bonding isconstituted similarly to the light emitting diode of wire bonding. Inthe case of a light emitting element based on nitride semiconductor, forexample, a plurality of nitride semiconductor layers including n-typeand p-type nitride semiconductor layers are formed one on another on oneof the principal surfaces of a transparent substrate, the p-sideelectrode is formed on the p-type nitride semiconductor layer (p-typecontact layer) located at the top and the n-side electrode is formed onthe n-type nitride semiconductor layer which is exposed by removing apart of the p-type nitride semiconductor layer, so that light isextracted from the other principal surface of the transparent resinlayer.

Example 1

In this Example, the light emitting device having the constitution shownin FIG. 1 was made by the following process.

(i) Die bonding/wire bonding

(ii) Line application of epoxy resin including YAG fluorescent materialmixed in a predetermined proportion.

(iii) Curing in a hot air oven

Curing condition: 150° C. for 4 hours

(iv) Forming the lens from transparent epoxy resin by transfer moldingprocess.

Transfer curing condition: 150° C. for 5 minutes (Mold temperature iscontrolled.)

(v) Releasing from mold and additional curing

Additional curing condition: 150° C. for 4 hours

(vi) Separating into individual devices by dicing

Comparative Example 1

As a comparative example, light emitting device having a singletransparent resin layer was made by the following process.

(i) Die bonding/wire bonding

(ii) Transfer molding of lens from epoxy resin including fluorescentmaterial mixed in a predetermined proportion.

Transfer curing condition: 150° C. for 5 minutes (Mold temperature iscontrolled.)

(iii) Releasing from mold and additional curing

Additional curing condition: 150° C. for 4 hours

(iv) Separating into individual devices by dicing

Light distribution characteristics of Example and Comparative Exampleare shown in FIG. 16A for the direction of 0° parallel to the mountingsurface (x direction in FIG. 3) and in FIG. 16B for the direction of 90°perpendicular to the mounting surface (y direction in FIG. 3). In FIG.16A and FIG. 16B, reference numeral 46 denotes the light distributioncharacteristic of the Example and reference numeral 48 denotes the lightdistribution characteristic of the Comparative Example. As can be seenfrom FIG. 16A and FIG. 16B, the Example of the present invention hasbetter directivity than the Comparative Example in both the direction ofWand the direction of 90°, and has higher luminous intensity (1.6 timesor more) in the normal direction. This is supposedly because thefluorescent material is dispersed in the entire transparent resin layerwherein the lens is formed in the Comparative Example, thus spreadingthe light through diffusion by the fluorescent material. In the Exampleof the present invention, in contrast, since the second transparentresin layer does not substantially include the fluorescent material,high directivity and high luminous intensity in the normal direction areachieved.

Example 2

In this Example, the light emitting device having the constitution shownin FIG. 4 was made similarly to the process of Example 1. In thisExample, samples were made with three variations of the lens shapeformed in the second transparent resin layer. The lens shape wascontrolled by means of the mold used in the transfer molding process.

Manufacturing conditions were set similarly to those of Example 1.

The samples of three kinds made as described above are shown insectional view in FIGS. 17A through 17C.

Initial optical and electrical characteristics of the samples 1 through3 were as follows.

TABLE 1 Luminous intensity Sample No. [mcd] x y Sample 1 672 0.281 0.266Sample 2 724 0.282 0.267 Sample 3 797 0.280 0.264

Light distribution characteristics of samples 1 through 3 are shown inFIG. 18A for the direction of 0° parallel to the mounting surface (xdirection in FIG. 3) and in FIG. 18B for the direction of 90°perpendicular to the mounting surface (y direction in FIG. 3). In FIG.18A and FIG. 18B, reference numerals 50, 52 and 54 denote the lightdistribution characteristic of the samples 1 to 3, respectively. Halfvalue angle (mean value) of the light distribution characteristic ofeach sample is shown in Table 2.

TABLE 2 Sample No. Direction of 0° Direction of 90° Sample 1 130 143Sample 2 114 140 Sample 3 96 136

The results described above show that a larger radius of curvature ofthe lens formed in the second transparent resin layer provides betterdirectivity and higher luminous intensity in the normal direction.

Example 3

In this Example, the light emitting device having the constitution shownin FIG. 10 was made by the following process.

First, a plurality of pairs of positive and negative electrodes wereformed from Cu/Ni/Ag on a substrate sheet that was made by laminatingepoxy resin sheets, and blue LEDs based on InGaN having emissionwavelength of 450 nm were mounted for each pair of electrodes. The LEDsand the electrodes were connected by wire bonding with gold wires.

The substrate sheet having the LEDs mounted thereon was placed in a moldof a compression molding machine that was heat to 120° C. Then liquidepoxy resin having YAG: Ce fluorescent material dispersed therein wasdripped onto the substrate sheet, and was cured at 120° C. for 600seconds in the mold of the compression molding machine. The liquid epoxyresin had initial viscosity of 1000 mPas and glass transitiontemperature of 140° C. The substrate sheet was then taken out of themold and was cured at 150° C. for 4 hours. Thus the light emittingdevice having the semi-cylindrical lens as shown in FIG. 10 wasobtained.

Comparative Example 2

As a comparative example, light emitting device was made by thefollowing process.

The process up to the mounting of the LED on the substrate sheet wassimilar to that of Example 1. Then the substrate sheet was placed in amold of a transfer molding machine that was heat to 150° C., and aliquid epoxy resin having YAG:Ce fluorescent material dispersed thereinwas poured, and was held for 300 seconds. The substrate sheet was thentaken out of the mold and was cured at 150° C. for 4 hours. Thus thelight emitting device having the semi-cylindrical lens as shown in FIG.10 was obtained.

(Comparison of Intensity of Light Emission)

Light distribution characteristics of the light emitting device ofExample 3 and Comparative Example 2 are shown in FIG. 19A for thedirection of 0° parallel to the mounting surface (x direction in FIG. 3)and in FIG. 19B for the direction of 90° perpendicular to the mountingsurface (y direction in FIG. 3). As can be seen from FIG. 19A and FIG.19B, the Example of the present invention has better directivity thanthe Comparative Example especially in the direction of 90°, and hashigher luminous intensity in the normal direction. This is supposedlybecause the fluorescent material is dispersed in the entire sealingresin layer, thus spreading the light through diffusion by thefluorescent material. In the Example of the present invention, since thesealing resin layer does not substantially include the fluorescentmaterial in the portion of lens, high directivity and high luminousintensity in the normal direction are achieved.

Comparison of Color Unevenness

Change in chromaticity with the direction of observation wasinvestigated on the light emitting devices of Example 3 and ComparativeExample 2. Changes in chromaticity coordinate x with the direction ofobservation are shown in FIGS. 20A and 20B, and changes in chromaticitycoordinate y with the direction of observation are shown in FIGS. 21Aand 21B. FIGS. 20A and 21A are graphs showing the change in chromaticityin the direction of 0° parallel to the mounting surface, and FIGS. 20Band 21B are graphs showing the change in chromaticity in the directionof 90° perpendicular to the mounting surface. As can be seen from FIG.20A, FIG. 20B, FIG. 21A and FIG. 21B, the Example of the presentinvention shows smaller change in chromaticity than the ComparativeExample does, especially in the direction of 90°, thus showing bettersuppression of color unevenness with different directions ofobservation. This is supposedly because the fluorescent material isdispersed in the entire sealing resin layer in the case of ComparativeExample, resulting in varying amount of fluorescent material transmittedby the light depending on the direction. In the Example of the presentinvention, in contrast, since the fluorescent material is concentratedin the vicinity of the light emitting diode 8, less color unevennessoccurs with different directions of observation.

The present invention has been fully described by way of preferredembodiments with reference to the accompanying drawings. It will beapparent for those skilled in the art that various variations andmodifications to the invention can be made. It is understood that suchvariations and modifications are included in the present invention tothe extent that they do not deviate from the scope of the presentinvention that is defined by the appended claims.

What is claimed is:
 1. A method for forming a light emitting device,said method comprising: forming a first transparent resin such that thefirst transparent resin covers one or more light emitting diodes mountedon a flat substrate, the first transparent resin having a heightmeasured from the flat substrate, to a top of the first transparentresin above one light emitting diode of the one or more light emittingdiodes, and the first transparent resin including a fluorescentmaterial; forming a second transparent resin so as to cover the firsttransparent resin, the second transparent resin having: a first heightmeasured from the flat substrate, to a top of the second transparentresin above one light emitting diode of the one or more light emittingdiodes, a second height measured from the flat substrate, to another topof the second transparent resin not located over the light emittingdiode, wherein said second height is a height of a portion of the secondtransparent resin having a flat upper surface, and the first height islarger than the second height of the second transparent resin, and theheight of the first transparent resin is larger than the second heightof the second transparent resin; and cutting through the flat substrateand the second transparent resin, to obtain a light emitting device. 2.The method as recited in claim 1, wherein the one or more light emittingdiodes are connected to respective conductive areas on the substrate viaone or more wires, and the one or more wires are covered by the firsttransparent resin.
 3. The method as recited in claim 1, wherein thefirst transparent resin has a semi-circular or semi-oval shape in across section perpendicular to the substrate, and the second transparentresin curves over the first transparent resin.
 4. The method as recitedin claim 1, wherein the second transparent resin is formed by transfermolding.
 5. The method as recited in claim 1, wherein the secondtransparent resin is formed by compression molding.
 6. The method asrecited in claim 1, wherein the first transparent resin is formed byprinting.
 7. The method as recited in claim 1, wherein the firsttransparent resin has a substantially rectangular shape.
 8. The methodas recited in claim 1, wherein the one or more light emitting diodes aremounted on the substrate by flip-chip bonding, the substrate being aninsulating substrate.
 9. A method for forming a light emitting device,said method comprising: forming a first transparent resin such that thefirst transparent resin covers one or more light emitting diodes mountedon a substrate, the first transparent resin including a fluorescentmaterial, wherein the one or more light emitting diodes are connected torespective conductive areas on the substrate via at least one wire, andthe first transparent resin covers said at least one wire, wherein saidat least one wire has a height which is measured from the substrate, toa highest part of said at least one wire above the substrate; forming asecond transparent resin so as to cover the first transparent resin, thesecond transparent resin having: a first height measured from thesubstrate, to a top of the second transparent resin above one lightemitting diode of the one or more light emitting diodes, a second heightmeasured from the substrate, to another top of the second transparentresin not located over the light emitting diode, wherein said secondheight is a height of a portion of the second transparent resin having aflat upper surface and the first height is larger than the second heightof the second transparent resin, and the height of said at least onewire is larger than the second height of the second transparent resin;and cutting through the substrate and the second transparent resin, toobtain a light emitting device.
 10. The method as recited in claim 9,wherein the first transparent resin has a semi-circular or semi-ovalshape in a cross section perpendicular to the substrate, and the secondtransparent resin curves over the first transparent resin.
 11. Themethod as recited in claim 9, wherein the first transparent resin has aconvex shape over the substrate.
 12. The method as recited in claim 9,wherein the second transparent resin is formed by transfer molding. 13.The method as recited in claim 9, wherein the second transparent resinis formed by compression molding.
 14. The method as recited in claim 9,wherein the first transparent resin is formed by printing.
 15. Themethod as recited in claim 9, wherein the first transparent resin has asubstantially rectangular shape.
 16. The method as recited in claim 9,wherein the one or more light emitting diodes are mounted on thesubstrate by flip-chip bonding, the substrate being an insulatingsubstrate.
 17. The method as recited in claim 9, wherein the firsttransparent resin completely covers said at least one wire.
 18. Themethod as recited in claim 9, wherein the first transparent resinpartially covers said at least one wire, and a top portion of said atleast one wire is not covered by the first transparent resin.